Spasmodic dysphonia (SD) is a disturbing disorder of laryngeal motor control, that although considered rare, has a profound impact on the communicative, social and vocational abilities of the individual. The use of botulinum toxin (BOTOX) injections as a treatment for SD has been supported by a number of researchers. The published studies in this area to date have focused on changes in acoustic and perceptual characteristics following BOTOX injections. Yet little attention has been focused on the broader impact of this form of treatment on the communicative abilities of these patients. To adequately address the effect of this disorder and its most popular treatment approach on the individual, a multi-dimensional approach to assessing its effectiveness in needed. One such approach is a three-tier model of chronic disease in which impairment, disability and handicap are assessed. To date, this, or any other model-based approach, has been applied to voice disorders. One of the goals of Healthy People 2000 is to reduce the proportion of people who experience a limitation in major activity due to a chronic disability (US Dept of HHS/PHS, 1990). Spasmodic dysphonia qualifies as a chronic disability so it is important to begin to utilize more comprehensive ways of characterizing this disorder and its impact on an individual. Therefore, exploration of the use of a model of chronic disease is timely and warranted. This research proposal will address the following question: What is the impact of spasmodic dysphonia and BOTOX treatment on the model of chronic disease? The specific aims of this project are: 1) to identify aerodynamic an respiratory measures that will reliably reflect the impairment related to SD, 2) to explore a measure of perceived vocal effort level as an indicator of functional limitation, 3) to refine a questionnaire designed to measure the perceived functional limitation of SD, 4) to identify measurement tools which may adequately track the outcome of intervention. Ten subjects with idiopathic spasmodic dysphonia will participate in several experimental protocols designed to characterize the impairment, functional limitation and disability associated with spasmodic dysphonia and the effect of BOTOX injections on these same indices. These same subjects will be followed longitudinally through a series of injections to determine the changes in the levels of the model that occur during treatment with BOTOX. It is expected that the information obtained from this investigation will suggest the relationships among the levels of a model of chronic disease.